1. Field of the Invention
The present invention relates to piezoelectric ceramic compositions and, more particularly, to piezoelectric ceramic compositions preferably used in ultrasonic motors, ultrasonic vibrators, piezoelectric actuators, and the like.
2. Description of the Related Art
It is preferable that the piezoelectric materials (piezoelectric ceramic compositions) used in ultrasonic motors, ultrasonic vibrators, piezoelectric actuators, and the like have a large mechanical quality factor, less heat generation during the application of a high voltage, a large piezoelectric constant, and a large amplitude of vibration.
Further, it is important for piezoelectric materials for ultrasonic motors to have stable temperature characteristics to be able to provide stable speed of rotation and torque.
For conventional piezoelectric ceramic compositions, however, it is difficult to keep both the mechanical quality factor and the piezoelectric constant sufficiently large, and the stability of the temperature characteristics is often not sufficient.
Piezoelectric ceramic compositions prepared to satisfy the above-described requirements as much as possible often have firing temperatures as high as 1200.degree. to 1300.degree. C.